In electrified vehicles, a high energy storage device provides traction power for motoring operations. In many cases the energy storage device is in the form of a high voltage battery, such as a lithium-ion battery, composed of a plurality of electrically coupled energy cells. Typically, a battery control module is coupled to a traction battery to monitor battery cell charge. To decrease test and evaluation costs, a battery simulator, rather than an actual traction battery, is often used to test a battery control module. A battery simulator is composed of a plurality of electronic devices designed to simulate the activity of a plurality of battery cells. To test a battery control module for a 36-cell battery, a battery simulator or battery tester designed to simulate 36 cells is used. A script based on a record of an actual vehicle drive cycle can be used put the simulator and control module through the fluctuating energy demands placed on an actual EV battery.
In the prior art, the capacity of a battery simulator to test a battery control module under a variety of operational conditions is somewhat limited by design constraints. For example, many simulators employ a low voltage power source that may only provide around 4-5 amps of current, much lower than the current typically provided by an actual traction battery. Some simulators, relying on very large sized capacitors to simulate energy storage capacity, may have slow response times when subjected to quick, random order testing. When optimized to better simulate vehicle dynamics and response times, a simulator may fail to represent energy storage capacity of a real battery cell. For example, simulators often provide lower energy pulses to a battery control module than those provided by an actual battery, reducing their effectiveness for hot plug testing of a battery control module. As a result, battery control modules that successfully pass tests conducted with a battery simulator are often damaged by inrush current when connected to an actual traction battery at a vehicle. Finally, battery simulators usually include a unidirectional DC converter configured to provide energy from the simulator to a control module, where the energy is typically dissipated as heat. Contemporary EV battery control modules can be designed for active self-balancing in which energy from one battery cell can be provided to a different battery cell. To test a battery control module configured for active self-balancing, it is desired that a battery simulator be configured to simulate the charge balancing process. Simulation of energy transfer between battery cells is not possible with prior art simulators designed to transfer energy only from a simulated cell to a battery control module.